1. Field of the Invention
The present invention relates to an ion implantation apparatus configured to perform a plurality of ion implantation processes to a same wafer successively.
2. Description of the Related Art
In a semiconductor production process, a process of implanting ions into a semiconductor wafer (hereinafter, it may be referred to as an “ion implantation process”) is generally performed for the purpose of changing the conductivity and/or the crystalline structure of the semiconductor and the like. An apparatus that is used in the ion implantation process is called an ion implantation apparatus and has a function of forming an ion beam by generating ions using an ion source and accelerating the generated ions and a function of transporting the ion beam to an implantation processing chamber and irradiating a wafer with the ion beam inside the implantation processing chamber.
In order to implant ions into an entire surface of a wafer as a processing target, a beam scanner causes an ion beam to scan in a reciprocating manner while the wafer reciprocates in a direction perpendicular to the beam scanning direction. At this time, the amount of the ion beam irradiated to each point of the wafer is controlled by changing a beam scanning speed or a reciprocating speed in accordance with the irradiation position of the ion beam on the wafer. Also, by performing an implantation process with a different wafer rotation angle plural times, a non-uniform dose amount distribution can be formed in a wafer plane.
Conventionally, in a case where the plural implantation processes are performed by changing the wafer rotation angle, an ordinary way is to perform ion implantation processing without changing a beam condition of an ion beam to be irradiated to a wafer between implantation processes so as to obtain a dose amount distribution formed in a desired rotationally-symmetric shape. If a dose amount distribution formed in a rotationally-asymmetric shape is to be obtained, the beam condition must be changed in each implantation process having a different wafer rotation angle, and a beam setup process for switching the beam condition will be required between implantation processes. It generally takes several tens of seconds to several tens of minutes for the beam setup process. If the beam setup process must be performed each time of changing the wafer rotation angle, this will significantly lower productivity of the ion implantation processing.